Mood disorders are generally classified by type and include, but are not limited to:
A morbid or clinical depression, which is usually diagnosed when sadness or elation is overly intense and continues beyond the expected impact of a stressful event. Symptoms often recur on an episodic basis or pursue a low-grade intermittent chronicity, which impairs the functioning of the sufferer.
Bipolar mood disorder, which commonly begins with depression and is characterised by periods of elation during the course of the illness.
Unipolar mood disorder, which is characterised as syndromal depression of episodes that last for typically 6 to 9 months.
The pharmaceuticals used in the treatment of Unipolar and Bipolar Mood Disorders can be grouped into three classes; the heterocylic antidepressants (HCAs), monoamine oxidase inhibitors (MAOIs) and lithium salts.
HCAs are the largest class of antidepressants and include tricyclic antidepressants such as imipramine. The HCAs have no immediate effect on euphoria and therefore have a low abuse potential. This group of antidepressants work by increasing the availability of the biogenic amines norepinephrine and/or serotonin (5-HT) by blocking re-uptake in the synaptic cleft. The side effects of HCAs include tachycardia, postural hypotension and cardio-toxicity. HCAs are also commonly associated with blurred vision, xerostomia, constipation, urinary hesitation, sedation and weight gain. The hypotensive side effects of HCAs often make them unsuitable for patients with mental disorders and the elderly.
MAOIs such as phenelzine are often prescribed for panic disorder. They work by inhibition of the oxidative deamination of the 3 classes of biogenic amines; noradrenergic, dopaminergic and 5-HT. MAOIs are underused because of clinicians' fears of paradoxical hypotension that may result from dietary or drug interactions, popularly known as the “cheese reaction” due to the high tyramine content in mature cheese. Other common side effects are postural hypotension erectile difficulties, anxiety, nausea, dizziness, insomnia, edema, weight gain and less commonly hepatotoxicity.
Lithium is used to stabilise the often unpredictable mood swings in bipolar mood disorder. The precise mechanism for its actions are unknown, but could be due to hyperpolarisation of the neuronal membrane. The most common acute benign side effects of lithium are tremor, fasciculation, nausea, diarrhoea, polyuria, polydipsia and weight gain. Lithium toxicity is more likely in elderly patients.